Ducklings need a good ballanced diet that includes 15- 20 % protien depending on their age as well as many vitamins and nutrients. While you can buy a multitude of ingredients to mix up something yourself- It is cheaper and easier in the long run to buy something manufactured for the purpose. There are many foods that can be added to a blanaced diet as treats- fruit and vegetables, meal worms, feeder fish- they should not be all that is fed to a growing duckling.